Preparation of organically modified organopolysiloxanes by a hydrosilylation reaction of a liquid organopolysiloxane having at least one silicon-hydrogen group per molecule with a non-silicone-containing, liquid organic compound containing at least one olefinic carbon-carbon double bond in each molecule is known.
SiC-bonded organomodified siloxanes, especially polyethersiloxanes, are an industrially very important substance class given their widely adjustable surfactant properties. The established route to preparation of these substances is the platinum metal-catalysed addition of siloxanes and silanes bearing SiH groups onto olefinically functionalized compounds, for example onto allyl polyethers.
The use of platinum catalysts for the addition of silanes or siloxanes having SiH groups onto compounds having one or more olefinic double bonds is known (hydrosilylation) and is described, for example, in the book “Silicon in Organic, Organometallic, and Polymer Chemistry” by Michael. A. Brook, publisher: John Wiley & Sons, Inc., New York 2000, page 403 ff., and in the patent literature, for example in DE-A-26 46 726, EP-A-0 075 703 and U.S. Pat. No. 3,775,452. In current industrial practice, predominantly hexachloroplatinic acid and cis-diammineplatinum(II) chloride have become established.
Even though it appears that this reaction principle is simple to describe in theory, reproducible performance on the industrial scale is very difficult.
Due to the phase incompatibility of the reactants (organopolysiloxane bearing SiH groups and organic compound containing an olefinic carbon-carbon double bond in each molecule), the hydrosilylation reactions conducted in a solvent-free manner commence from a biphasic state. This is especially true of the preparation of SiC-bonded polyethersiloxanes. Without introduction of considerable shear energy, the reaction mixtures without solvent typically have a tendency to separation of their reactant phases.
As a consequence of the observed incompatibility of the reactant phases, the hydrosilylation reactions conducted in a solvent-free manner often run very slowly, sometimes even incompletely, and hence impair the space-time yield achievable in the production and in some cases also reduce the product quality achievable.
The more hydrophilic the unsaturated polyether to be added on, the greater the phase incompatibility between the reactants. This finding is therefore especially applicable to polyethers having a high proportion of ethylene oxide in their molecular structure.
The application-related usability of products originating from the platinum metal-catalysed addition reaction of siloxanes bearing SiH groups onto compounds having olefinic double bonds is especially directly linked to the conversion achieved in the hydrosilylation, i.e. the minimization of residual SiH functions. Residual SiH, especially in the presence of ubiquitous traces of water (for example air humidity), leads to uncontrollable hydrolysis and crosslinking processes which, specifically in the case of addition compounds of high molecular weight, necessarily lead to gelation and make the products unusable.